Secondary battery having cathode tab of pin type

ABSTRACT

A secondary battery includes an electrode assembly where a negative plate and a positive plate are arranged by interposing a separator therebetween, and a can mounting the electrode assembly therein. A cap assembly is fitted to the can to tightly seal the can, and is electrically connected to the positive plate. A pin is inserted into the electrode assembly, and it contacts the negative plate and the can to electrically interconnect the negative plate and the can.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and benefit of Korean Patent Application No. 2003-39960 filed on Jun. 19, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

[0002] (a) Field of the Invention

[0003] The present invention relates to a secondary battery, and in particular, to a cathode tab for a negative plate of an electrode group.

[0004] (b) Description of Related Art

[0005] Generally, batteries are largely classified into a secondary battery which can be repeatedly charged and discharged, and a primary battery which is not rechargeable, and is disposed of after it becomes depleted. Batteries are formed with various shapes, such as a cylindrical shape, a prismatic shape, and a pouch shape, depending upon the profile of the target appliances.

[0006] Among them, the cylindrical-shaped secondary battery has an electrode assembly where a negative plate and a positive plate are rolled in the form of a jelly-roll while interposing a separator therebetween, a cylindrical can mounting the electrode assembly therein, and a cap assembly fitted to the top of the can.

[0007] An insulating plate is disposed between the electrode assembly and the cap assembly as well as between the electrode assembly and the can.

[0008] The positive plate of the electrode assembly is electrically connected to the cap assembly via an anode tab, and the negative plate of the electrode assembly is electrically connected to the can via a cathode tab.

[0009] The cathode tab is mainly formed with a nickel strip having a thickness of 0.05-0.1 mm, and it is welded to the negative plate located at the outermost area of the electrode assembly and the inner bottom surface of the can to electrically interconnect the negative plate and the can.

[0010] However, as the nickel strip used as the cathode tab is rigid, when the electrode assembly welded with the cathode tab is inserted into the can, the cathode tab is liable to be stuck at the opening portion of the can, thereby incurring an abnormality in the arrangement of the electrode assembly.

[0011] In this connection, the outer diameter of the electrode assembly is designed such that when the electrode assembly is inserted into the can, a margin (for instance, of 0.2-0.4 mm) is allowed between them. However, this makes the electrode assembly limited in its dimensions, and hence, the electrode assembly cannot be enlarged within the can enough to heighten the battery capacity.

SUMMARY

[0012] According to one embodiment of the invention, the secondary battery includes an electrode assembly where a negative plate and a positive plate are arranged by interposing a separator therebetween, and a can mounting the electrode assembly therein. A cap assembly is fitted to the can to tightly seal the can, and is electrically connected to the positive plate. A pin is inserted into the electrode assembly, and it contacts the negative plate and the can to electrically interconnect them.

[0013] The pin is formed with a hollowed shape in one embodiment, protrusions are formed at one side end portion of the pin, and the protrusions are welded to the can. In the embodiment, the protrusions are inclined toward the center of the pin.

[0014] A plurality of the protrusions are provided in another embodiment of the invention, and communication holes are arranged between the protrusions to communicate the interior of the pin with the exterior thereof.

[0015] In one embodiment, the pin comprises nickel or nickel alloy.

[0016] In another embodiment, the electrode assembly is substantially in the shape of a jelly-roll, and the pin is inserted into the center of the electrode assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other advantages of the present invention will become more apparent by describing exemplary embodiments thereof in detail with reference to the accompanying drawings in which:

[0018]FIG. 1 is a sectional view of a secondary battery according to an embodiment of the present invention;

[0019]FIG. 2 illustrates the structure of a pin according to the embodiment of the present invention;

[0020]FIG. 3 is a schematic perspective view of an electrode assembly for the secondary battery according to the embodiment of the present invention; and

[0021]FIG. 4 illustrates another embodiment of a pin according to the present invention.

[0022]FIG. 5 illustrates yet another embodiment of a pin according to the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0023] The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

[0024] As shown in FIGS. 1 to 3, the secondary battery has an electrode assembly 10 where a negative plate 12 and a positive plate 14 are rolled in the form of a jelly-roll while interposing a separator 13 therebetween, a cylindrical can 20 mounting the electrode assembly 10 therein and being electrically connected to the negative plate 12 of the electrode assembly 10, a cap assembly 30 fitted to the top of the can 20 and being electrically connected to the positive plate 14 of the electrode assembly 10, and a pin 50 inserted into the center of the electrode assembly 10 while contacting the negative plate 12 and being partially welded to the bottom surface of the can 20 to electrically interconnect the negative plate 12 of the electrode assembly 10 and the can 20.

[0025] The pin 50 can be formed with a hollowed shape for obtaining a passageway for gas. Alternatively, as shown in FIG. 4, the pin 50 may be formed with a solid bar shape.

[0026] A plurality of communication holes 53 are formed at the bottom end portion of the pin 50 to communicate the interior of the pin 50 with the exterior thereof and obtain the passageway for gas and electrolyte, but the formation thereof is not necessary (as shown in FIG. 5).

[0027] A plurality of protrusions 52 are formed at the bottom end portion of the pin 50 between the neighboring communication holes 53 while defining those holes.

[0028] The protrusions 52 are welded to the can 20 while contacting the bottom surface thereof, and are inclined toward the center of the pin 50. This structure makes it easy to weld the protrusions 52 to the bottom surface of the can 20 at one point. Alternatively, as shown in FIG. 5, only one protrusion may be formed at the bottom end portion of the pin 50 without forming the holes 53.

[0029] Meanwhile, the pin 50 is formed with nickel or nickel alloy, which involves excellent conductivity and excellent weldability with respect to the can 20.

[0030] As shown in FIG. 3, with the electrode assembly 10, the negative plate 12, the separator 13, the positive plate 14, and the separator 13 are sequentially tired from the interior of the assembly to the exterior thereof, and rolled in the form of a jelly-roll.

[0031] Consequently, the negative plate 12 is exposed at the interior of the electrode assembly 10, and is closely adhered to the pin 50 mounted within the electrode assembly 10 to make an electrical connection thereto.

[0032] The cap assembly 30 has a cap 32 and a cap cover 34 fitted to the can 20 by interposing a gasket 38 therebetween. A rubber vent 36 is provided between the cap 32 and the cap cover 34.

[0033] An anode lead 15 connected to the positive plate 14 of the electrode assembly 10 is connected to the cap cover 34 of the cap assembly 30.

[0034] An upper insulating plate 40 is installed between the cap assembly 30 and the electrode assembly 10, and a lower insulating plate 42 is installed between the bottom surface of the can 20 and the electrode assembly 10.

[0035] The cap assembly 30, the electrode assembly 10, and the can 20 may be constructed using the structure of a common lithium ion battery, and hence, detailed explanation thereof will be omitted.

[0036] With the above-structured secondary battery, a cathode tab is not installed at the exterior of the electrode assembly, and hence, it is possible to form the electrode assembly with an outer diameter corresponding to the inner diameter of the can.

[0037] Accordingly, with the inventive secondary battery, when the outer diameter of the electrode assembly is 17.10-17.20 mm, it is possible to enlarge the outer diameter of the electrode assembly by 0.5-1.0% compared to the conventional one, and hence, to increase the battery capacity by 2-5%.

[0038] Furthermore, as the cathode tab is not installed at the exterior of the electrode assembly, the cathode tab is prevented from being stuck on the can during the process of inserting the electrode assembly into the can, and hence, the assembling operation is performed in a very fluent manner.

[0039] With the conventional case, as the center portion of the electrode assembly is vacant with a weak strength, it is liable to be distorted under the application of external impact. By contrast, with the inventive secondary battery, a pin is provided at the center of the electrode assembly, and it absorbs the force of an external impact, thereby preventing the electrode assembly from being distorted.

[0040] Furthermore, with the conventional case, when the electrode assembly is tested within a hot oven at 150° C. or more, the inner structure thereof is distorted so that the gas internally generated is not easily discharged through the safety vent provided at the bottom of the can, and is liable to explode. By contrast, with one embodiment of the inventive secondary battery, as the passageway of gas is fluently made through the pin, the gas that is internally generated is well discharged through the safety vent, thereby preventing the battery explosion, and satisfying safety concerns.

[0041] The secondary battery according to the embodiment of the present invention may be formed with a cylindrical shape, a prismatic shape, or other shapes.

[0042] Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concept herein taught which may appear to those skilled in the art will still fall within the spirit and scope of the present invention, as defined in the appended claims. 

What is claimed is:
 1. A secondary battery comprising: an electrode assembly where a negative plate and a positive plate are arranged by interposing a separator therebetween; a can mounting the electrode assembly therein; a cap assembly fitted to the can to tightly seal the can, and being electrically connected to the positive plate; and a pin inserted into the electrode assembly, and contacting the negative plate and the can to electrically interconnect the negative plate and the can.
 2. The secondary battery of claim 1, wherein the pin is substantially hollow.
 3. The secondary battery of claim 2, further comprising protrusions located at one end of the pin and welded to the can.
 4. The secondary battery of claim 3, wherein the protrusions are inclined toward the center of the pin.
 5. The secondary battery of claim 4, further comprising communication holes arranged between the protrusions to communicate the interior of the pin with the exterior thereof.
 6. The secondary battery of claim 1, wherein the pin comprises at least one of nickel and nickel alloy.
 7. The secondary battery of claim 1, wherein the electrode assembly is substantially in the shape of a jelly-roll, and the pin is located in the center of the electrode assembly.
 8. The secondary battery of claim 1, wherein the shape of the can is substantially cylindrical. 